The present invention relates to a mechanical method to create a variable stagger and camber airfoil.
For power generation applications, limits on start time, grid demand response time, and maintenance factors create an environment where it is often advantageous to reduce the output of the gas turbine rather than shutting it down as demand is reduced. Axial flow industrial gas turbines modulate output levels by controlling the amount of air flow entering the compressor with inlet guide vanes.
The conventional “Inlet Guide Vane” (IGV) is a single stage of articulated airfoils (about a radial axis) located in the front of the axial flow compressor. The maximum amount of air flow occurs when the IGV chord is aligned, or parallel, with the incoming air flow. This flow is reduced as the IGV stagger angle is rotated to a more aerodynamically closed position. For purposes of the disclosure, the stagger angle (ΘStagger) is defined as the angle between the air flow velocity vector and a straight line which connects the leading and trailing edge of the interconnected airfoils in the chordwise direction. The IGV operation is simple, but aerodynamically inefficient. In this regard, industrial gas turbines are designed to operate most efficiently at full power. As the output level is reduced, by limiting the incoming air flow the efficiency is also reduced. This efficiency loss is attributable to the aerodynamic inefficiencies associated with a conventional IGV configuration.
Conventional variable geometry compressor airfoils are limited to either stagger-only or camber-only changes. See in this regard U.S. Pat. No. 5,314,301 and U.S. Pat. No. 4,995,786. Thus, conventional variable geometry compressor airfoils do not have both variable camber and stagger control.